Lua Table - Search for Items that starts with an Letter - lua

Question

i have this table
animals = {
{sname = "bunny", name = "bunny hase", size = 4, size2 = 8, size3 = 9},
{sname = "mouse", name = "Micky Mouse", size = 1, size2 = 12, size3 = 22},
{sname = "cow", name = "Die Kuh", size = 30, size2 = 33, size3 = 324
}
there i can search by a listed entry
for _,v in pairs(animals) do
if v.sname == "bunny" then
print(v.sname, v.name, v.size, v.size2, v.size3)
break
end
end
and get the result:
bunny bunny hase 4 8 9
Now i want to search in my table by starting with a single Letter, for example "b", that show me all the entries starting with the letter "b" to get the same result?
I found no Solution. May you can help me?

Answer 1

First: The table animals needs a trailing } ;-)
Put it in a Lua -i console and play around with...
>animals = {
{sname = "bunny", name = "bunny hase", size = 4, size2 = 8, size3 = 9},
{sname = "mouse", name = "Micky Mouse", size = 1, size2 = 12, size3 = 22},
{sname = "cow", name = "Die Kuh", size = 30, size2 = 33, size3 = 324}
}
-- Now set a __call metamethod on same table
>setmetatable(animals,{__call=function(tab,...)
local args={...}
for key, value in pairs(tab) do
if value.sname:find(args[1],1) then print(key,'=',value.sname) end
end
end})
table: 0x565c4a00
-- Lets try it once
>animals('b')
1 = bunny
-- Next one
>animals('c')
3 = cow
-- Last one
>animals('m')
2 = mouse
Using metatables holds your stuff together.
Another fine place is the __index metamethod that can hold all functions you need for that table and can be used like the string functions on a string.
( Like: value.sname:find(args[1],1) )
This leads to the heart of what find should do.
In first example it looks in whole sname for a matching pattern.
Check the Lua patterns what also can be useful.
Maybe a ^ only for the begining sounds smart?
So construct the find pattern: '^'..args[1]
...and use more than one letter if you have a cow, crow, frog and fish in your animals.
Example with function name find in __index
>animals = {
{sname = "bunny", name = "bunny hase", size = 4, size2 = 8, size3 = 9},
{sname = "mouse", name = "Micky Mouse", size = 1, size2 = 12, size3 = 22},
{sname = "cow", name = "Die Kuh", size = 30, size2 = 33, size3 = 324}
}
-- Place a find function into __index
>setmetatable(animals,{__index={find=function(tab,...)
local args={...}
for key, value in pairs(tab) do
if value.sname:find('^'..args[1]) then print(key,'=',value.sname) end
end
end}})
table: 0x565c3db0
-- first
>animals:find('c')
3 = cow
-- next
>animals:find('m')
2 = mouse
-- last
>animals:find('b')
1 = bunny
If you like to print all key values then extend the print() in find().

Answer 2

Stop, i found an issue....
Look here - i prefer the first solution:
animals = {
{sname = "bunny", name = "bunny hase", size = 4, size2 = 8, size3 = 9},
{sname = "mouse", name = "Micky Mouse", size = 1, size2 = 12, size3 = 22},
{sname = "cow", name = "Die Kuh", size = 30, size2 = 33, size3 = 324}
}
-- Now set a __call metamethod on same table
setmetatable(animals,{__call=function(tab,...)
local args={...}
for v,k in pairs(tab) do
if k.sname:find(args[1],1) then print(v,'=',k.sname) end
end
end})
-- Search Entries with Start U.....
-- there should be no result, but....
animals('u')
i get the Result:
1 = bunny
2 = mouse
that should not be the result!